Sodium hypochlorite is a highly effective bleaching agent and has long been used in conjunction with soaps and detergents to remove stains and other types of soils in the laundering of fabrics. It is generally formulated at a concentration of about 4-8% in water for sale for household use, where it is typically diluted to a concentration of about 200 ppm sodium hypochlorite for laundry bleaching.
Optical brighteners are dyes which are absorbed by fabrics and impart to the fabric an added increment of whiteness/brightness by means of their ability to absorb invisible ultraviolet radiation and re-emit it as visible radiation. Optical brighteners have been included as a component in laundry products for many years.
Most optical brighteners are subject to chemical attack by hypochlorite in solution, and their brightening effect is considerably diminished when used in conjunction with hypochlorite in laundering of fabrics. However, some optical brighteners have been developed which are highly resistant to hypochlorite attack.
It is desirable to formulate concentrated (typically about 4-8%) sodium hypochlorite solutions which contain bleach stable optical brighteners. Thus, if the housewife uses bleach in conjunction with a detergent which contains a brightener which is not stable to hypochlorite, a fabric brightening effect will still be obtained from the brightener present in the bleach.
Optical brighteners are generally insoluble in concentrated hypochlorite, and tend to quickly settle to the bottom of an aqueous hypochlorite product. Thus, simple addition of optical brightener to concentrated aqueous hypochlorite results in a product which must be vigorously shaken each time before use. Because of the tendency for rapid settling, even vigorous shaking before each use does not necessarily always result in the obtaining of uniform proportions of brightener and hypochlorite in each use. U.S. Pat. No. 3,393,153, Zimmerer, issued July 16, 1968, presents a solution to this problem by including in the composition a particulate material such as colloidal silica or a particulate colloidal polymeric resin which keeps the optical brightener in suspension in aqueous hypochlorite.
It is an object of the present invention to prepare aqueous compositions containing hypochlorite and finely suspended optical brighteners, without the use of added particulate colloidal materials to provide brightener suspension.